Addressing emerging nutrient limitations in the Australian grains industry for improved fertiliser management of potassi

Australia has a negative K balance of 400kt per year with approximately 3 times more K removed from the system than applied across agricultural areas (Norton 2017). The continuous negative K balance through consecutive time periods has increased the area of cropping considered marginal or deficient for K. The impacts of running a negative K balance, and how to best manage this issue, has been raised at NGN forums across all GRDC regions. K deficiency has historically been a problem associated with sandy soils, however increasing instances of deficiency have been seen in heavier textured soils across all regions.
In the Southern region, yield responses of 0.55-2.0 t/ha have been shown in small plot trials in heavier textured soils with K levels above critical test values. This suggests growers may be leaving yield in the paddock due to K deficiency. In addition to high removal rates in grain, K is lost in stubble burning, through hay or stubble removal, via leaching and can become stratified in (dry) topsoil layers following subsoil uptake. The shift to no-till farming exacerbates stratification of K in heavier textured soils where K from plant residues is stranded in the top few centimetres where it bonds with minerals and clay particles. The Cation Exchange Capacity (CEC) of the soil and the extent of other minerals such as Ca and Mg have a very large impact on K availability to plants and its mobility. Consequently, the K fertiliser placement strategies developed for sandy soils with low CEC will have lower K use efficiency (KUE) in heavy textured soils with high CEC.
To improve K nutrient management, growers need access to tools and knowledge to identify when they may or are likely to have K deficiency. They also need to know where this problem is occurring (which crop species or what part of the landscape) and have the management strategies to address the issue and maximise return on their fertiliser investment. Soil testing is one such tool, but it needs to accurately represent plant available K. The current method (Colwell K) for determining plant available K and associated critical soil test values for maximum yield work well in lighter textured soils but are not as representative for heavier textured soils with high CEC values found through the GRDC Northern and Southern regions. Whilst improved critical K levels have been developed for the Northern region, they require further validation across soil types and regions. This provides an opportunity to consolidate and build on the current body of K research across all three regions. It targets two key components that require RD&E to improve growers' confidence in K fertiliser management to maximise return on investment (ROI):
* the tools required to identify paddocks and regions at risk of K deficiency across diverse soil types (different CEC levels and mineralogy) in the GRDC Southern and Northern regions,
* fertiliser management strategies tailored to soil types and climatic regions (K rate, placement and formulation) to match crop demand with nutrient availability and maximise ROI.
GRDC's strategic analytics partnership, Analytics for the Australian Grains Industry (AAGI) can offer the following analytics support as a GRDC in-kind contribution: 1) fit-for-purpose experimental design advice accounting for multiple treatment and environmental factors; and 2) multi-site/factor analyses to support development of soil K critical values and guidelines. To access one or more aspects of the available support, applicants must enquire with AAGI directly and describe the proposed support scope in their tender. The tender description should include an estimate of workload (e.g., FTE) and in-kind valuation provided by AAGI. Successful applicants will be required to complete an Analytical Collaboration Plan to specify the data to be provided to AAGI and the analytics support AAGI will provide. A sample plan template is available from AAGI.
Please make enquiries to the University of Queensland, attn. Dr Elizabeth Meier at [email protected]. Please note, applicants that decline AAGI support and propose their own support/resources must provide a technical and value-for-money rationale for not using in-kind AAGI support.